1. Field of Invention
The present invention relates to a backlight module of a liquid crystal display (LCD), and more particularly, to a light guide plate and an edge-lit backlight module utilizing the same.
2. Description of Prior Art
The design of an LED's backlight is improved along with the improvement of LED's efficiency, from the earliest four-side type into a two-side type, then into a one-side type, the present technology and the direction of future development focus on a single-short-side type.
With the development of 3D technology, a TV with a 3D display function is also gradually becoming a mainstream. Currently the 3D display modes include shutter (Shutter Glass), polarized FPR (Film-type Patterned Retarder) and other manners.
Shutter-style 3D needs to be achieved by the scanning backlight with a panel pixel scanning. Backlight sources are usually partitioned. LEDs of an edge back-lit style LED light bar are divided into sets to correspond to a plurality of subsections of a screen. When the first frame signal scans the first subsection, the LEDs corresponding to the first subsection are lighted up, and the rest of the LEDs are turned off. When the signal scans the second subsection, only the LEDs corresponding to the second subsection are lighted up. The rest can be deduced accordingly. Such operations are necessary to be conducted for every frame. The display performance of the shutter-style 3D depends on a crosstalk between the subsections and timing setting.
The crosstalk between the subsections related to the backlight mainly comes from the effect of the brightnesses of the different subsections. In the best situation, when the LEDs correspond to one subsection are lighted up, the backlight sources of the other subsections all present a dark mode. FIG. 1 is a side-view of a light guide plate with microstructures of a prior art. It is a common design to dispose saw-shaped microstructures 13 on the light emitting plane 11 of the light guide plate 10. The microstructures 13 on the light guide plate 10 destroy the condition of light total reflection with different geometric shapes. FIG. 2 is a light distribution diagram of a flat light guide plate of a prior art and a light guide plate with wave-shaped micro structures of another prior art. It is clearly observed that the light guide plate with wave-shaped micro structures has a more convergent light distribution than the flat light guide plate, but in practice, it is impossible to restrain the divergence of light with only micro structures.
Further refer to FIG. 3, which is a vertical direction brightness distribution diagram when a common light guide plate with micro structures is lighted up in one LED light source. The width corresponds to the light source (100% brightness) is a point, the width of FWHM (Full Width at Half Maximum; 50% brightness) apparently increases. With further refer to FIG. 4, which is a diagram showing the width of FWHM at different distances from the light source. In a single-short-side edge-lit manner, as the distance increases, the FWHM increases accordingly, which means the crosstalk is more serious at a far side than a light incident side of the single-short-side edge-lit light guide plate.
FIG. 5 is a top view drawing of a backlight module of a prior art. A backlight module 20 comprises a first LED bar 23, a second LED bar 24 and a light guide plate 21. The light guide plate 21 divides into a plurality of long-shaped subsections (R1-R4) which are perpendicular to the first LED bar 23 according to the scanning mode. The meaning of the subsections is the first LED bar 23 and the second LED bar 24 both comprises a plurality of LED light sources. The LED light sources of the first LED bar 23 are divided into several groups of LED light sources, each group of LED light source corresponds to each subsections (R1-R4). Each group of the first LED bar 23 could be on or off, the second LED bar 24 has the same arrangement. With the arrangement of light on certain group of LED light source as above to achieve lighting the certain subsection of the light guide plate 21. But there is crosstalk phenomenon occurs on the board line between the subsections.
In order to solve the crosstalk between subsections, a plurality of circle scattering dots 22 are formed on the light guide plate 21 of the backlight module, the scattering dots have the same interval between each other, and controlling the divergence of light by the change of size of the circle scattering dots 22.
FIG. 6 is a top view drawing of a backlight module of another prior art. The backlight module 30 comprises a first LED bar 33, a second LED bar 34 and a light guide plate 31. The difference to FIG. 5 is a plurality of long-shaped scattering dots 32, the long-shaped scattering dots 32 have the same interval, and controlling the divergence of light by the change of length of the circle scattering dots 32 parallel to the first LED bar 33.
Moreover, the divergence of light could be controlled by the same size of scattering dots, different interval. But, there is still certain crosstalk between the subsections even combining the above 3 kinds of scattering dots applying on the light guide plate, the reason is the angle of light is inevitably divergent while the light entering into the light guide plate, by the arrangement of scattering dots mentioned above is still impossible to control the divergence of light effectively.